sounds like you have the white nylon piston head which has the steel ring then an O ring then the buffer washer behind it which believe it or not was once upon a time rubber they always look like old nasty oily leather when they are stripped due to age the nylon heads always seem to be tighter than the later alloy ones, some say the nylon heads expand over time causing a tighter fit, I have in the past just wet and dry sanded them until they slip in nicely, keeps the piston head smooth too